1. Field of the Invention
The present invention relates to dehumidification systems. More particularly, the present invention relates to industrial-type dehumidifiers having a heat pump, receiver/dryer, and closed-cycle regeneration. Additionally, the present invention relates to dehumidifiers in which the receiver/dryer relies on energy used for dehumidification instead of heat transfer.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
Air humidity control has historically been important in providing comfortable working and living environments and for the preservation of assets, such as historical documents. Recently, it has become even more critical for certain environments, such as hospital operating theaters, electronics manufacturing facilities and pharmaceutical production process areas. In addition, humidity control improves the economics of refrigeration on, for example, supermarket display cases, by eliminating or reducing defrost cycles or the use of the anti-sweat heater.
Basic humidity reduction is typically accomplished at the cooling coil of an air conditioning system. If the coil temperature is below the dew point of the air stream entering the coil, excess moisture collects on the coils, producing a condensate stream. In such a system, the goal is control of the air stream temperature, with some reduction in humidity. In contrast, by adding a sensor to measure humidity (humidistat), air is cooled as needed, in response to the humidistat, to maintain a desired humidity level. Such systems provide either temperature control or humidity control, but not both. A separate heating or cooling system must be added in series with the humidity control coil to achieve both temperature and humidity control. This can increase energy costs. For example, often the cooling necessary to reach a desired humidity results in overcooling the air stream, requiring subsequent reheating of the air stream to achieve the desired temperature and humidity. Some systems are able to alleviate energy cost penalty by using waste heat elsewhere in the system (e.g., condenser heat). However, the components necessary to reclaim the waste heat and transfer it to the air stream add to the installation cost of the system. Where low-humidity conditions are needed, coil temperatures must be correspondingly low. If the coil temperature is maintained by a vapor compression system, the compressor must work harder and use more energy to reach the lower temperature, resulting in a reduced chiller coefficient of performance (COP).
Other mature technologies exist for dehumidification, other than by a cooling coil. Desiccant wheels and enthalpy wheels, honeycombed wheels having surfaces covered with a solid desiccant, such as silica gel, are often used to remove moisture from an air stream. The wheels rotate between supply and exhaust air streams to transfer water and heat between them. Desiccant wheels can achieve very low dew points by using a heated exhaust air stream to greatly enhance the removal of adsorbed water, creating a very dry desiccant for contact with the supply air stream. Such a system needs a lot of energy to heat the exhaust air and additional cooling of the supply air stream to remove heat transferred from the exhaust air to the wheel and subsequently to the supply air stream. In contrast, enthalpy wheels have a lighter coating of desiccant and are primarily designed to transfer energy in the forms of heat (sensible heat) and moisture (latent heat) from one stream to another without any additional energy. The amount of moisture removed depends on the dryness of the exhaust air. As such, enthalpy wheels are more limited than desiccant wheels regarding the level of humidity control they can maintain. Combinations of desiccant and enthalpy wheels, along with the use of waste heat from elsewhere or water for evaporative cooling, can improve the level of humidity control as well as the energy efficiency of the system, but at a significant penalty in initial cost and complexity of the system.
Liquid desiccant dehumidifiers are another currently available alternative for removing moisture from air. A hygroscopic fluid (one that readily adsorbs water from the air), such as a LiCl solution, circulates between supply and exhaust air streams. The solution picks up moisture from the supply air stream, essentially diluting the solution, which then circulates to the exhaust air stream where heat evaporates the excess moisture into the exhaust air stream. In addition to the energy needed to heat the liquid to evaporate the moisture on the exhaust air side, additional energy is necessary on the supply air side to remove the heat of condensation either by sub-cooling the liquid before contact with the supply air or by cooling the supply air after dehumidification. As with the systems discussed above, to ease this energy penalty, waste heat from elsewhere can be used to evaporate the moisture, at higher initial cost and complexity for the system.
In the past, various patents have issued relating to liquid desiccant dehumidification systems. For example, U.S. Pat. No. 4,939,906, issued on Jul. 10, 1992 Spatz et al., describes a multi-stage boiler/regenerator for liquid desiccant dehumidifiers. In this system, a gas-fired desiccant boiler and a combined desiccant regenerator/interchange heat exchanger is used. The combined re-generator/heat exchanger utilizes steam produced from the boiler to provide heat for partial regeneration. The desiccant boiler has a liquid/vapor separator chamber and a thermosyphon recirculation to reduce scale and corrosion of the boiler.
U.S. Pat. No. 5,213,154, issued on May 25, 1993 to Marsala et al., shows a liquid desiccant regeneration system for use in an air-conditioning system. The regeneration system utilizes a falling film heat exchanger for transferring heat from concentrated desiccant so as to dilute the desiccant. A boiler is used for regenerating dilute desiccant. Piping is provided for flowing the dilute desiccant from the air-conditioning system upward through the heat exchanger. A flow path directs the concentrated desiccant from the boiler through the heat exchanger into the air-conditioning system. This patent only relates to an exchanger used in a regeneration process. It does not relate to a entire dehumidification system.
U.S. Pat. No. 6,514,321, issued on Feb. 4, 2003 to Lehto et al., describes a dehumidification system utilizing desiccants and multiple effect evaporators. The desiccant the solution from the multiple effect evaporator is conveyed to a desiccant spray chamber that sprays the cooled desiccant solution into an airstream. The desiccant solution absorbs water vapor from the air stream creating a desiccant and water solution. A conduit transfers the water and desiccant solution to the multiple effect evaporator for removal of the water from the desiccant solution.
U.S. Pat. No. 7,938,888, issued on May 10, 2011 to G. Assaf, teaches a liquid desiccant regenerator system including a desiccant/air heat exchanger having a first desiccant inlet and a desiccant reservoir. The reservoir has a first desiccant outlet, a second desiccant outlet and a second desiccant inlet. The first desiccant inlet and the first desiccant outlet are connectable to a heat source. The second desiccant inlet conducts diluted desiccant of the reservoir and the second desiccant outlet conducts concentrated desiccant from the reservoir. The second desiccant inlet and the desiccant outlet are connected to a desiccant/desiccant heat exchanger for applying heat to the diluted desiccant flowing into the reservoir. Water is heated with moisturized hot air and the heat of this water is transferred into the internal environment in order to generate water by condensing the moisturized hot water in regeneration. Water releasing its energy is then transferred into the same chamber to be used in order to cool the moisturized hot air. In this manner, thermal energy is transferred into the environment. This system is carried out with a heating or cooling of the environment.
U.S. Pat. No. 8,268,060, issued on Sep. 18, 2012 to Hargis et al., provides a dehumidifier system having a dehumidifier section within which liquid desiccant absorbs moisture from air flowing therethrough and a dehumidifier section within which the desiccant is regenerating that employs a heat exchanger for maintaining a relatively high temperature differential between the desiccant contained within the dehumidifier and the regenerator sections. The desiccant is conducted to either the dehumidifier section or the regenerator section and is separated into multiple streams. The multiple streams are treated differently from one another before being discharged to preselected segments of the air flow moving through the corresponding one of the dehumidifier section and the regenerator section. This process is realized with a heat pump between regeneration (with external environmental air) and dehumidifying (with internal environmental air). The system requires external environmental air. Additionally, the system requires thermal energy transfer into the internal environmental air.
U.S. Patent Publication No. 2010/0090356, published on Apr. 15, 2010 to Sines et al., teaches a liquid desiccant dehumidifier in which a liquid desiccant solution is used to extract moisture from ambient air in a first location within a dehumidifier. A regenerator is in fluid communication with the dehumidifier so as to extract moisture from the liquid desiccant solution. One or more pumps circulate the liquid desiccant through the dehumidifier. One or more pumps also circulate the liquid desiccant through the regenerator. The base exposes the liquid desiccant solution at least partially to the ambient air.
U.S. Patent Publication No. 2011/0132027, published on Jun. 9, 2011 to Gommed et al., describes a liquid desiccant dehumidification system and heat/mass exchanger therefor. The exchanger has an absorber solution section operably connected to the system's absorber/dehumidification system and a desorber solution section operably connected to the desorber/regeneration section. A partition separates the sections and includes at least two interconnecting ports positioned to facilitate flow of a relatively weak solution from the absorber solution section into the desorber solution section.
U.S. Patent Publication No. 2013/0269522, published on Oct. 17, 2013 to D. D. DeValve, is a heat pump-enabled desiccant dehumidification system that includes a heat pump with a desiccant-coated passive heat transfer device on both sides of the heat pump and an air circulation system for alternately directing a process airstream to be humidity controlled and a separate regenerative airstream past each side. As desiccant on one side becomes laden with moisture, the air streams are redirected to the opposite sides of the heat pump so the regenerative stream removes moisture from the first side. Simultaneously, the airstream to be humidity-controlled uses the previously regenerated desiccant on the second side.
International Publication No. WO/2013/172789, published on Nov. 21, 2013 to Cai et al., describes a dehumidifying system having a dehumidifier containing a desiccant for dehumidifying a process airflow and a regenerator to regenerate the desiccant. The dehumidifier has a cooler connected to the dehumidifier. The cooler is designed to cool the desiccant such that the desiccant is cooled by the cooler before entering the dehumidifier. The regenerator has a heater connected thereto. The heater is designed to heat the desiccant such that the desiccant is heated by the heater before entering the regenerator. A desiccant transfer conduit is connected to the dehumidifier and the regenerator and a desiccant supply conduit is connected to the dehumidifier and the regenerator such that the desiccant transfer conduit and the desiccant supply conduit form a desiccant transfer loop through the dehumidifier and the regenerator such that the desiccant loop provides transfer of desiccant from the dehumidifier to the regenerator via the desiccant transfer conduit and supply of desiccant from the regenerator to the dehumidifier via the desiccant supply conduit. The regeneration air is not in a closed cycle. Cooling is provided by receiving thermal energy from the internal environment.
It is an object of the present invention to provide a dehumidification system which recovers energy before discharge of volatile and hot air.
It is another object of the present invention provide a dehumidification system in which heat is not transferred to the outside environment.
It is a further object of the present invention to provide a dehumidification system whereby energy is used only for the purpose of dehumidification.
It is another object of the present invention provide a dehumidification system that uses a heat exchanger such that the outgoing/incoming liquid transfers the energy to each other.
It is another object of the present invention to provide a dehumidification system whereby the liquid is transferred long distances in the plastic pipes so as to allow the liquid to work with dehumidification terminals in independent zones.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.